1. Field of the Invention
The present invention relates to a light receiving module used for an optical fiber communication and a manufacturing method of the light receiving module, in particular to such a light receiving module providing a good and uniform optical couple especially in case of a plurality of optical fibers in array.
2. Related Background Art
Light receiving modules disclosed in "IEICEJ Technical Report, Vol. 91, No. 201 (OQE91-60 to 68)" published by Institute of Electronics Information and Communication Engineers are conventionally known. FIG. 1 and FIG. 2 show structures of them.
According to the light receiving module of FIG. 1, an IC chip 6 in which a pre-amplifier circuit is formed and a light receiving element 4 are placed inside a lower package 2, an optical fiber 8 is vertically fixed to an upper package 10, where a distal end of the optical fiber faces the light receiving face of the light receiving element 4, and the lower package 2 and the upper package 10 are hermetically sealed to prevent light from leaking into the module.
And the module receives a light transmitted through the optical fiber 8 on the light receiving element 4 and converts the light signal to an electrical signal. Further, the electrical signal is amplified by the pre-amplifier circuit in the IC chip 6 and is output through a lead terminal 12.
According to the light receiving module of FIG. 2, an IC chip 18 in which a pre-amplifier circuit is formed and a light receiving element 16 are placed inside a package 14 which has a hermetically sealed construction to prevent light from leaking into the module, where a distal part of the optical fiber 20 is arranged in parallel with the light receiving face of the light receiving element 16. The distal end of the optical fiber 20 is cut slantingly and polished, so that light transmitted through the optical fiber 20 is reflected by the polished face 22 and is admitted in the light receiving face of the light receiving element 16.
And, the electrical signal, converted from the light signal in the light receiving element 16, is amplified by the pre-amplifier circuit in the IC chip 18 and is output through a lead terminal (not shown in the drawing).
However, in the conventional light receiving modules of the constructions described above, an IC chip, a light receiving element and an optical fiber are arranged and fixed independently each other in a unit. Namely, precision of facing location between the optical fiber and the light receiving element is governed by precision of location of each component, resulting in wide dispersion of light receiving sensitivity or difficulty in manufacturing modules within predetermined tolerances or light receiving sensitivity since the modules should be fabricated tuning the location of each component one by one. Consequently, productivity of the modules could not be improved.
Especially, in a light receiving module in which a plurality of optical fibers and a plurality of corresponding light receiving elements are set in array for doing a parallel communication, optical couples between the optical fibers and the light receiving elements should be good and uniform through out all of the combinations, which requires a very high mechanical precision. Consequently, it was very difficult to accomplish a good productivity from the point of yield rate, etc.